Effect of output current ripple on the input supply current and the power quality for a cycloconverter-fed drive

The assessment of the impact of a cycloconverter-fed drive on the supply system and the improvement of its quality depends on the correct estimation of the generated input supply current harmonics/interharmonics. The analytical derivation of an expression for the input current of an ideal cycloconverter load has as yet neglected the output current ripple. For higher output to input frequency ratio, however, the cycloconverter generates low frequency interharmonic output current of such appreciable magnitude that it necessitates a proper estimation method for the input supply current considering output current ripple. The analytical derivation of the input current spectra as available in the classical literature is extended to consider, for the first time, the effect of output current ripple on the input supply current frequency spectra. The analytical derivation is validated with simulation results as well as with experimental results for a cycloconverter-fed synchronous motor drive. It is shown how by considering the output ripple, the power quality indices of the system become poorer than those estimated without considering the output current ripple.